Grid structure for high frequency apparatus



Nov. 4, 1941. w. w. HANSEN r-:rAL

GRID STRUCTURE FOR HIGH FREQUENCY APPARATUS Filed July 22, 1959 2 Sheets-Sheet l INVENTORJ WML/AM W HANSEN Il RUSSELL H /AR/AN l. I B JH W00@ YARD ATTORNEY.

Nov. 4, 1941. w. W. HANSEN ETAL GRID STRUCTURE FOR HIGH FREQUENCY APPARATUS Filed July 22, 1939 2 Sheets-Sheet 2 F D. l

F/[nll F/Em INVENTORS W/LL/A 'M W HA NsEN RUSSELL H. VA R/A N J a /v 5 TTORNEY.

Patented Nov. 4, 1941 UNITED STATES PATENT' OFFICE GRID STRUCTURE FOR HIGH FREQUENCY APPARATUS Application July 22, 1939, Serial No.- 285,878

(Cl. Z50-27.5)

2 Claims.

This invention relates, generally, to grid structures for use in connection with high frequency radio apparatus. and the invention has reference, more particularly, to novel grid structures of this character and to the method of making the same, said grid structures having relatively small electron intercepting areas, whereby electron streams may be passed therethrough with but small loss of electrons.

Considerable diiiiculty has been experienced with grids heretofore used for controlling the passage of streams of electrons, due to the tendency of these grids to overheat in use. Such grids have generally had a relatively large electron intercepting area acting to block an appreciable portion of the electrons of a stream passing therethrough, resulting not only in a considerable decrease in the efficiency of the circuits employed, but also resulting in excess heating and consequent distortion of the grids due to the collision of the electrons therewith.

The principal object of the present invention is to provide a novel grid structure and method of making the same, which structure is so constructed as to have an extremely small electron intercepting area sc as to pass a stream of electrons with but small loss of electrons thereof due to collision with the grid, the said grid structure being formed of highly conducting electrical material for enabling the ready flow of high frequency currents thereby and providing effective shielding against electric elds.

Another object ofthe present invention is to provide a novel grid structure having grid bars that are preferably flat members oriented with their edges facing the source of electrons, the said bars being of material having high heat conductivity, to thereby enable the heat produced by collision of electrons therewith to be rapidly dissipated from the grid, so that the same remains relatively cool in use.

Still another object of the present invention is to provide a novel grid structure that is produced by a novel method of casting, whereby extremely thin grid bars are produced that are not appreciably contaminated by the material of the mold, said grid bars having relatively large depth and hence rigidity, so that any tendency of the grid to warp due to heat is largely eliminated, the said grid structure as a whole having high mechanical rigidity and being adapted to be so designed that thermal expansion is allowed for without setting up excessive stresses in the grid members or bars.

Still another object of the invention is to provide a novelA grid structure that is adapted to transmit streams of electrons having specified degrees of divergence or convergence, with small loss by interception by the grids of the electrons in the streams.

Still another object of the present invention is to provide a novel grid structure that is eective in limiting the amount of angular divergence of electron streams, where desired, the grid structure being relatively deep for effecting this purpose, the depth of the grid structure also greatly enhancing the strength thereof.

Other objects and advantages will become apparent from the specification, taken in connection with the accompanying drawings wherein the invention is embodied in concrete form.

In the drawings,

Fig. 1 is an enlarged perspective view, with parts broken away, of a mold suitable for use in casting a grid according to the process of the present invention.

Fig. 2 is a vertical sectional view of a form of apparatus suitable for use in carrying out the method.

Fig. 2A is an enlarged plan view of a novel grid embodying the principles of the present invention.

Fig. 3 is an enlarged perspective view of a somewhat different type of mold for use in forining grids of different configuration from that shown in Fig. 2A.

Fig. 4 is an enlarged fragmentary perspective view of a somewhat different type of grid strucure.

Fig. 5 is a view similar to Fig. 2A, but discloses a different type of grid having certain advantages in the manner of allowing for thermal expansion and contraction.

Figs. 6, 7 and 8 are enlarged fragmentary plan views of various modified grid structures.

Fig. 9 is an enlarged plan view of the radial type grid with large central aperture.

Fig. 10 is a view similar to Fig. 9, but showing a grid wherein the central aperture is reduced 1n size.

Fig. 11 illustrates a plan view of a grid adapted for use with divergent or convergent beams, and

Fig. 12 is a sectional view taken along line A-A or B-B of Fig. l1.

Similar characters of reference are used in all of the above figures to indicate corresponding parts.

Referring now to Figs. l and 2A of the drawings, the reference numeral I designates a mold Aout so as to surround the cross grooves 2. The

slots produced in the peripheral edge portion 4 of the mold due to the cutting of slots 2 are then lled, as by use of welding material or other suitable means.

In casting the grid structurein the mold I, the latter is placed in a suitable container such as the sealed container III of Fig. 2, wherein a vacuum or an inert or reducing atmosphere is maintained as by the use of nitrogen or hydro-- gen. In order that the grid shall have high electrical and heatnconductivity, the same should be cast from a suitable material, such as copper, gold or silver. Thus, the mold I may be placed upon an electric heater II within container Il and heated for receiving the casting material, such as copper, which is placed in a crucible I2 and heated by the electric heater I3 until molten, where upon the arm Il carrying the crucible I2 is revolved so as to pour the molten ccpper upon the mold I.

Just as soon as the molten copper has filled the mold I, cooling fluid, such as water from a tank I3', is supplied as through pipe Il' to chill the mold and the cast grid so as to prevent the iron of the mold from appreciably dissolving in and contaminating the copper grid, which would result if the mold Vand casting were allowed to cool gradually, such gradual cooling resulting in adecrease in the electrical conductivity of the grid. In the structure of Fig. 2, the cooling water isadapted to flow through the space provided between mold I and heater II to eifect im mediate chilling of the mold and grid. Ihereafter the mold with the grid therein is removed by opening cover I5. V

It has been found that in casting the grid in a gaseous atmosphere, such as hydrogen, gas bubbles are apt to be trapped in the narrow grooves 2, vthus producing an imperfect casting. This trouble is of course entirely eliminated if the grid is cast in vacuum. It is very important in performing the casting operation that the metal being cast, such as copper, should wet the mold in which it is cast. In ordinary casting processes, the molten metal does not wet the mold and therefore, of course, could` not penetrate into ne cracks suchas-I, due to the fact that the surface tensionv of'. the molten metal prevents it from entering such ne grooves or cracks. By using iron for the mold, the molten copper will wet the mold and the metal will `be drawn 'into the small grooves or cracks 2 by capillary action, and provided no bubbles are trapped in these ilne grooves, the mold will be completely lled, thereby forming a perfect grid.

' The grooves 2 are of substantial depth as comthe mold away by means of a. suitable chemical.

Thus, if the mold I is made of a metal of the iron group and the casting metal is copper or silver, the iron mold can be dissolved with no ill effects on the copper or silver grid structure by use of a non-oxidizing acid, such as hydrochloric. This is true because the iron will disf place hydrogen from an acid, forming an iron salt, whereas the copper and silver in the presence of iron will not be appreciably affected by hydrochloric acid and similar non-oxidizing acids. Thus, by placing the mold and its contained cast grid in a suitable hydrochloric acid solution over night, the iron mold will be completely dissolved away. leaving the novel grid structure of this invention, as shown in Fig. 2A, wherein the cross bars 5 and 5' are extremely thin transversely, though of appreciable depth.

Inasmuch asmilling cutters having a thickness as little as six-thousandths of an inch may be used in cutting the grooves 2 of the mold I, it will be apparent that the cross bars or webs l, 5' of the finished grid Il will be extremely thin and hence the grid as a whole will have a very low electron intercepting-cross sectional area. Instead of using copper or silver, a metal such as aluminum may be used, in which case'an oxidizing acid such as nitric acid may be used, if desired, for dissolving away the mold I. If desired, the thin webs or bars 5, 5' of the grid, which, as above stated, may be of the order of six-thousandths of an inch, may be made even thinner by use of a suitable etching fluid, such as ferrie chloride. In order to obtain uniform etching, the grid is placed in the etching solution and the latter is preferably continuously agitated to circulate rapidly through all the grid interstices. Even though the bars 5, 5' are thus made tissue thin, their relatively great depth together with the reenforcing action of the grid frame I! serves to render the same strong and highly resistant to injury. y

A type of mold is shown in Fig. 3 for producing grids having hexagonal grid openings, although this type of mold may be used for producing grids having openings of other configuration. In this figure. a plurality of hexagonal bars i, corresponding in number to the number of apertures' in the grids, are assembled with fiat metal spacers 1 and 8 at the ends. It will be noted that the upright deformed flat metal spacers 'I serve to space the' bars transversely from each other a thickness corresponding to the desired thickness of the vertical webs or bars of the finished grid structure. whereas the msverse spacer strips I serve to space the t vertically `the desired distances for forming the transverse grid bars or webs of the grid. Wires I are shown wrapped around the bundle of rods I so as to maintain the same in assembled condition. Thereafter, this mold is placed in a suitable cylindrical receptacle providing a hollow cavity having a shape corresponding to the depared with theirwidth, in order to render the v the mold from the grid it is necessary to dissolve eres tightly to the v sired exterior shape of the grid, the assembly being then placed in the evacuated container Il ofFig. 2 and'metal poured in around thebars i so as to -ll the receptacle. The mold and contained grid is then rapidly chilled as before, whereupon the mold is withdrawn from the container and the end portions thereof containing the spacer strips I and [which are preferably of the same material as the bars l, such as iron. are cut off and the. remaining stock is cut up into grids of any desired thickness. The iron is then dissolved away from the grid structures,

as by use of hydrochloric acid, the metal lying between the cylindrical container and the bars 6 providing the peripheral ring portion of the grid structure.

In making the novel form of grid structure shown in Fig. 4, wherein certain of the grid bars are made much deeper and somewhat thicker than the remainder, a mold somewhat similar to that of Fig. 1 is used, with the exception that certain of the slots are made deeper and wider than the remainder, thereby producing an exceedingly strong grid structure which has high heat conductivity. This grid also has a low intercepting cross sectional area and is especially desirable in those installations where the electrons of the stream are not all moving exactly parallel to each other, as is often the case.

The form of grid shown in Fig. 5 is designed to withstand high thermal expansions and contractions due to temperature variations over the area thereof. This grid is made up of a series of progressively smaller concentric rings 22, 22 and 22" which are interconnected by bars 23 and 23' that are inclined to the radii of the rings, i. e., arranged somewhat in the form of spirals. In casting this grid, the mold used may conveniently be made in three parts, a first ringlike outer part having an annular groove in the face thereof for forming the outer frame or ring 22, together with spaced slots which are approximately spirally inclined for forming the bars 23; a second ring-like part having an annular slot at its periphery for cooperating with the rst part in forming the annular intermediate frame or ring 22', said second part also having spirally inclined slots for forming the bars 23'; and a circular third part having an annular groove in its face for cooperating with the second part to form the inner annular ring 22", said third part having radial slots for forming the radial bars 23". The two inner parts have a tight fit in the outer or first part so that when the mold is assembled and the casting metal poured, the grid formed will have the configuration shown in Fig. 5. The grid casting metal, such as copper, is cast as before mentioned, either in a vacuum or in the presence of an inert gas or a reducing atmosphere, the metal wetting the iron or other mold to thereby obtain a very well defined grid structure, the bars 23, 23' and 23" of which, together with frames or rings 22' and 22" being ordinarily very thin. When this type of grid structure is put in use, heating thereof due to electron bombardment causes the bars 23, for example, to lengthen somewhat, thereby eecting a twist of the intermediate frame or ring 22'. Similarly, bars 23' will lengthen, effecting a twist of the inner frame or ring 22", this elongation and twisting taking place without any serious strain being imposed upon the grid structure. In ordinary grid structures, where no provision is made for expansion and contraction of the webs or bars, repeated heating and cooling will tend, in time, to effect the breaking of the bars.

In the forms of the invention shown in Figs. 6, 7 and `8, grids of the type shown in Fig. ZIA may be rst prepared and then the cross bars or webs 25, 25' and 25" thereof deformed somewhat, as by use of -a peg or pegs inserted into the interstices of the grid and the latter then pushed sideways, thereby effecting an initial distortion of the grid bars and causing them to assume a substantially sinuous contour or shape, whereby ating large stresses and strains therein. Obviously, the cross bars may be deformed into various configurations, as shown in these iigures.

In the form of the invention shown in Fig. 9, the grid consists of an annular member I6 having a plurality of radially inwardly directed grid bars or lingers I I which are mutually spaced from one another, said bars terminating short of the center of the grid structure, thereby providing an internal central aperture I8.

The form of the invention shown in Fig. 10 is very similar to that shown in Fig. 9, except that certain of the grid bars, designated I9, are made longer than others, designated 20, thereby enabling the central aperture I8' to be made much smaller than that provided in Fig, 9.

The grid structures of Figs. 9 and 10 have decided advantages in use ln that heat is conducted from the grid bars by the shortest possible path and also the high frequency charging currents used take the shortest possible path in moving to and from the grid. These types of grid structures will also pass either convergent or divergent streams of electrons with substantially no additional loss by collision with the grid due to the convergence or divergenceA of the stream, provided that tne streams are convergent or divergent about a perpendicular axis passing through the center of the grid. In these grids, of course, no stresses are set up in the grid bars due to heating, since they are free to expand and contract.

These grids may be made by sawing longitudinal slots in the periphery of a cylindrical iron bar, which bar is then placed in a cylindrical cavity provided in a suitable receptacle and the cast metal poured therein, i. e., between the bar and the receptacle. The receptacle is then removed and the bar is sawed up into slices or longitudinal portions and the iron dissolved out, as by the use of hydrochloric acid, as previously described.

In the form of the invention shown in Figs. 11 and 12, the grid structure is illustrated as having cross bars 2| which are all arranged converging with respect to the longitudinal axis of the grid structure. This type of grid is especially desirable for converging or diverging electron streams and may be made in the same manner as that described in connection with Figs. 1 and 2 except that the slots are milled at progressively increasing angles with respect to the longitudinal or central axis of the mold, thereby obtaining the structure shown in Fig. 12.

Of course, in all forms of the invention shown, the grid bars may be made even thinner than that produced by casting by use of a suitable etching solution, as described in connection with the structure of Fig. 2. Owing to the great depth with which these grids may be cast, their frontal cross sectional area may be reduced to a minimum while still retaining great strength and rigidity in use.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A grid structure for use with electron streams, comprising a grid frame and a plurality of intersecting grid bars spanning the space within said frame, said grid bars being formed integral with said frame and with one another and having relatively great depth in comparison with their thickness, said bars being deformed so as to have substantially sinuous contours, whereby thermal expansion and contraction thereof eiect transverse deflections oi the bars without unduly y stressing the same,

2. A grid structure for use with electron streams comprising an open grid frame and a plurality of grid bars of the depth of said frame extending inwardly therefrom and coacting with WILLIAM W. HANSEN. RUSSELL H. VARIAN. JOHN R. WOODYARD. 

